For my waves and diffraction course we have had a completely incompetent lecturer. We were looking at standing waves and then all of a sudden he spent a lecture looking at attenuation, not mentioning where it would apply or explaining it particularly well. I have tried to find a text book to explain what is going on but have been fairly unsuccessful. Can anyone point me in the right direction for materials to explain what is going on. I have hopefully attached the single slide he used in the lecture.